Cables used for submersible pumps are mainly applied in submersible pumps which usually operate underground at a depth of thousands of meters. The submersible pumps operate in harsh conditions in the oil wells, generally in environments in high temperature and high pressure and containing highly corrosive oil gases. The strength, durability and corrosion resistance of submersible pump cables are highly required. The submersible pump cables in the prior art have the following technical problems.
1. Insufficient Strength
The submersible pump cables are likely to break during the usage due to a large length and certain loads borne on the cables. To solve this problem, in the prior art, an armor layer or coiled tubing is usually provided on an outer side of the cable.
2. Low Duration and Corrosion Resistance
A common plastic sheath is provided in the outermost layer of the conventional submersible pump. Generally, a submersible pump will continuously operate underground for a long period of time. During the maintenance, the cables are found damaged. By cutting apart the used cables, it is often found that the damage of their sheaths allows liquid to enter the interior of the cables, and at a high temperature, the polypropylene insulating layer swells; and since the swollen insulating layer becomes soft and is decreased in its insulating strength, the core shift of the copper wire is caused, and as a result, local cable breakdown occurs.
For example, Chinese Patent Application 201610312692.2 disclosed a suspension-mountable submersible pump cable comprising a plurality of leads, a filling layer, a sheath layer and an armor layer, where each lead consists of a conductor located in the middle, an insulating layer wraps the conductor, and an oil-proof gasket layer surrounds the insulating layer; the plurality of leads are stranded together; a filler is filled between the leads and the filler wraps the plurality of leads to form the filling layer; and the sheath layer wraps the filling layer and the armor layer wraps the sheath layer.
Chinese Patent Application 201521065012.9 disclosed a submersible pump cable with two armor layers, where a tight insulating layer is provided around a copper conductor, a tight sheath layer is provided around an insulating layer, and the sheath layer is wrapped by an oil-proof gasket layer; and then three wire cores of such a structure are arranged side by side to form a first steel-tape armor layer, and then a second steel-tape armor layer is formed outside the first steel-tape armor layer.
Chinese Patent Application 201410098616.7 disclosed a circular submersible pump cable comprising a support core, a plurality of leads, a polytetrafluoroethylene wrapping layer, an oil-proof layer, a sheath layer and an armor layer, where each lead comprises a conductor located in the middle and an insulating layer wrapping the conductor; the cable core is wrapped by the polytetrafluoroethylene wrapping layer which is then wrapped by the oil-proof layer; and the oil-proof layer is wrapped by the sheath layer which is then wrapped by the armor layer.
With regard to the above submersible pump cables, an armor layer is provided outside the cables. This can fulfill the requirement on strength. However, since the armor layer is generally made of metal material, it is easily corroded by stratum corrosive media, especially hydrogen sulfide. Furthermore, this increases the production cost and is inconvenient to use.
Chinese Patent 201210283869.2 disclosed a longitudinal pressure-resistant sealed submersible pump cable with a stranded conductor, comprising a stranded conductor located in the central portion of the cable, and further comprising an insulating layer wrapping the stranded conductor, where the stranded conductor comprises a central conductor and surrounding conductors which are all stranded together; and a semi-conductive rubber filler is provided between the central conductor and the surrounding conductors. In this patent, the ointment filler in the conventional cables is replaced with the semi-conductive rubber. The possibility for the ointment to change into liquid from solid at normal temperature is avoided. In this solution, the weight of the cables is to be borne by their conductors. Therefore, the cables are quite easy to break due to their limited bearing capacity, and accordingly, it is impossible to produce a very long cable. Furthermore, the cables are less corrosion-resistant since the conductors are wrapped by a common insulating layer. And, due to the bearing requirement, the insulating layer must have a very large thickness which is almost ⅓ of the radius of the cables. The effective working space of the cables is heavily occupied by an insulating layer of such a large thickness, and the waste of space is caused. Therefore, such a cable is low in universal applicability.
Accordingly, in the prior art, there is a need for a cable used for submersible pump which can fulfill the requirements on both high bearing capacity and high corrosion-resistant performance.